2. You may remember
from the other day
• Maxwell proposed that visible light consists of
electromagnetic waves.
• Planck suggested that atoms and molecules emit
energy only in discrete quantities
• Bohr stated the electrons in atoms can only exist
in specific energy shells
• Quantum – the smallest quantities of energy that
can be emitted in the form of electromagnetic
radiation.
3. E = h
• E = Energy (J)
• h = Planck’s Constant
= 6.626x10-34 J s
• = Frequency (1/s)
4. The Photoelectric Effect
• 1905 – Albert Einstein
• Photoelectric Effect
• Threshold Frequency
• Beam of light behaves
like a stream of particles.
• Photons
• E = h
Beam
me up
Scottie
!
6. What is he talking about?
Bohr, “Electrons are quantized.”
Science, “Why?”
Bohr, “I don’t know.”
7. Louis DeBroglie has the Answer!
DeBroglie – Light behave like a
standing wave.
Node – A point on a standing wave
that does not move. Its amplitude
is zero.
Particle and Wave properties are
related.
= h / mu
8. VERY IMPORTANT
EQUATIONS
1. u =
(ulight = c = 3.00x108 m/s)
2. E = h
(h = 6.63x10-34 J s)
3. = h/mu
(m = mass, u = velocity)
10. VERY IMPORTANT
EQUATIONS
1. u =
(ulight = c = 3.00x108 m/s)
2. E = h
(h = 6.63x10-34 J s)
3. = h/mu
(m = mass, u = velocity)
Editor's Notes
Photoelectric Effect – electrons are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency, called the threshold frequency.
Beam of light behaves like a stream of particles.
Photons – Particles of Light
Einstein deduced that each photon must possess energy, E given by the equation E = h
___________________________________
Transition: Einstein paved the way for future scientists to understand emission spectra
Emission Spectra – either continuous or line spectra of radiation emitted by substances.
Emission spectra of atoms in the gas phase produce bright lines in different parts of the visible spectrum.
Line Spectra –Light emission only at specific wavelengths.
Niels Bohr (1913) – Electrons move around atom’s nucleus, like planets around the sun. Orbitals were quantized such that jumping from one orbital to the next required a specific amount of energy.
Ground State – The lowest, most stable energy state of a system
Excited State – Any state higher in energy than the ground state
